Catalytic Asymmetric Synthesis of N‐Chiral Amine Oxides

Direct asymmetric synthesis of N‐chiral amine oxides was accomplished (up to 91:9 e.r.) by means of a bimetallic titanium catalyst. A hydroxy group situated at the γ‐position of the N stereocenter enables the desired N‐oxidation through dynamic kinetic resolution of the trivalent amine substrates. The method was further extended to the kinetic resolution of racemic γ‐amino alcohols with a preexisting stereocenter, giving an important class of enantioenriched (up to 99.9:0.1 e.r.) building blocks that are otherwise difficult to synthesize.     

Enantioselective Synthesis of Functionalized Arenes by Nickel‐Catalyzed Site‐Selective Hydroarylation of 1,3‐Dienes with Aryl Boronates

A catalytic method for the site‐selective and enantioselective synthesis of functionalized arenes by the intermolecular hydroarylation of terminal and internal 1,3‐dienes with aryl pinacolato boronates is reported. The reactions are promoted by 5.0 mol % of a readily available monodentate phosphoramidite‐Ni complex in ethanol, affording a variety of enantioenriched products in up to 96 % yield and 99:1 er. Mechanistic studies indicate that Ni–allyl formation is irreversible and related to the nature of the arylboronate.     

One‐Pot Synthesis of Lactams from Cycloalkanes and tert‐Butyl Nitrite by Using N‐Hydroxyphthalimide as Key Catalyst

Lactams were successfully synthesized in the one‐pot reaction of cycloalkanes and tBuONO in the presence of N‐hydroxyphthalimide as a key catalyst. Cyclododecane and cyclohexane were treated with tBuONO followed by triethylamine and then cyanuric chloride in a one‐pot manner to give laurolactam and ε‐caprolactam, respectively, in good yields. The Beckmann rearrangement of oximes by cyanuric chloride was found to be accelerated by the use of 1,1,1,3,3,3‐hexafluoro‐2‐propanol as solvent. The method provides the first successful environmentally benign direct synthetic route to lactams from cycloalkanes without the formation of any salt.     

Synthesis of Chiral Tertiary Boronic Esters by Oxime‐Directed Catalytic Asymmetric Hydroboration

Chiral boronic esters are useful intermediates in asymmetric synthesis. We have previously shown that carbonyl‐directed catalytic asymmetric hydroboration (CAHB) is an efficient approach to the synthesis of functionalized primary and secondary chiral boronic esters. We now report that the oxime‐directed CAHB of alkyl‐substituted methylidene and trisubstituted alkene substrates by pinacolborane (pinBH) affords oxime‐containing chiral tertiary boronic esters with yields up to 87 % and enantiomeric ratios up to 96:4 e.r. The utility of the method is demonstrated by the formation of chiral diols and O‐substituted hydroxylamines, the generation of quaternary carbon stereocenters through carbon–carbon coupling reactions, and the preparation of chiral 3,4,4‐trisubstituted isoxazolines.     

Catalytic Wittig Reactions of Semi‐ and Nonstabilized Ylides Enabled by Ylide Tuning

The first examples of catalytic Wittig reactions with semistabilized and nonstabilized ylides are reported. These reactions were enabled by utilization of a masked base, sodium tert‐butyl carbonate, and/or ylide tuning. The acidity of the ylide‐forming proton was tuned by varying the electron density at the phosphorus center in the precatalyst, thus facilitating the use of relatively mild bases. Steric modification of the precatalyst structure resulted in significant enhancement of E selectivity up to >95:5, E/Z.     

Nickel‐Catalyzed Alkyl–Alkyl Cross‐Couplings of Fluorinated Secondary Electrophiles: A General Approach to the Synthesis of Compounds having a Perfluoroalkyl Substituent

Fluorinated organic molecules are of interest in fields ranging from medicinal chemistry to polymer science. Described herein is a mild, convenient, and versatile method for the synthesis of compounds bearing a perfluoroalkyl group attached to a tertiary carbon atom by using an alkyl–alkyl cross‐coupling. A nickel catalyst derived from NiCl₂?glyme and a pybox ligand achieves the coupling of a wide range of fluorinated alkyl halides with alkylzinc reagents at room temperature. A broad array of functional groups is compatible with the reaction conditions, and highly selective couplings can be achieved on the basis of differing levels of fluorination. A mechanistic investigation has established that the presence of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) inhibits cross‐coupling under these conditions and that a TEMPO–electrophile adduct can be isolated.     

Synthesis of Non‐Classical Arylated C‐Saccharides through Nickel/Photoredox Dual Catalysis

The development of synthetic tools to introduce saccharide derivatives into functionally complex molecules is of great interest, particularly in the field of drug discovery. Herein, we report a new route toward highly functionalized, arylated saccharides, which involves nickel‐catalyzed cross‐coupling of photoredox‐generated saccharyl radicals with a range of aryl‐ and heteroaryl bromides, triggered by an organic photocatalyst. In contrast to existing methods, the mild reaction conditions achieve arylation of saccharide motifs while leaving the anomeric carbon available, thus providing access to a class of arylated glycosides that has been underexplored until now. To demonstrate the potential of this strategy in late‐stage functionalization, a variety of structurally complex molecules incorporating saccharide moieties were synthesized.     

Facile,Catalytic Dehydrocoupling of Phosphines Using β‐Diketiminate Iron(II) Complexes

Catalytic dehydrocoupling of primary and secondary phosphines has been achieved for the first time using an iron pre‐catalyst. The reaction proceeds under mild reaction conditions and is successful with a range of diarylphosphines. A proton acceptor is not needed for the transformation to take place, but addition of 1‐hexene does allow for turnover at 50 °C. The catalytic system developed also facilitates the dehydrocoupling of phenylphosphane and dicyclohexylphosphane. A change in solvent switches off dehydrocoupling to allow hydrophosphination of alkenes.